Lemkau PV. The 1933 and 1936 studies on the prevalence of mental illnesses and
symptoms in the eastern health district of Baltimore, Maryland. In: Weissman MM, Myers JK, Ross CE, eds. Community
Surveys of Psychiatric Disorders. New Brunswick, NJ: Rutgers University
Press; 1986:23-39.

Context Social causation (adversity and stress) vs social selection (downward
mobility from familial liability to mental illness) are competing theories
about the origins of mental illness.

Objective To test the role of social selection vs social causation of childhood
psychopathology using a natural experiment.

Design Quasi-experimental, longitudinal study.

Population and Setting A representative population sample of 1420 rural children aged 9 to
13 years at intake were given annual psychiatric assessments for 8 years (1993-2000).
One quarter of the sample were American Indian, and the remaining were predominantly
white. Halfway through the study, a casino opening on the Indian reservation
gave every American Indian an income supplement that increased annually. This
increase moved 14% of study families out of poverty, while 53% remained poor,
and 32% were never poor. Incomes of non-Indian families were unaffected.

Main Outcome Measures Levels of Diagnostic and Statistical Manual of Mental
Disorders, Fourth Edition, psychiatric symptoms in the never-poor,
persistently poor, and ex-poor children were compared for the 4 years before
and after the casino opened.

Results Before the casino opened, the persistently poor and ex-poor children
had more psychiatric symptoms (4.38 and 4.28, respectively) than the never-poor
children (2.75), but after the opening levels among the ex-poor fell to those
of the never-poor children, while levels among those who were persistently
poor remained high (odds ratio, 1.50; 95% confidence interval, 1.08-2.09;
and odds ratio, 0.91; 95% confidence interval, 0.77-1.07, respectively). The
effect was specific to symptoms of conduct and oppositional defiant disorders.
Anxiety and depression symptoms were unaffected. Similar results were found
in non-Indian children whose families moved out of poverty during the same
period.

Conclusions An income intervention that moved families out of poverty for reasons
that cannot be ascribed to family characteristics had a major effect on some
types of children's psychiatric disorders, but not on others. Results support
a social causation explanation for conduct and oppositional disorder, but
not for anxiety or depression.

The association between poverty and mental illness has been described
throughout the world and throughout history.1- 9 Clinicians
and researchers have noted the difficulty of untangling the effects of "social
causation, . . . adversity and stress associated with low social statuses"
from those of "social selection, [which] posits that genetically predisposed
persons drift down to or fail to rise out of" poverty.10

Recent research has emphasized the role played by genetics in an individual's
vulnerability to a wide range of psychiatric disorders. Social selection is
an example of a theory consistent with gene-environment correlation, in that
affected individuals, and often their family members with them, drift down
into poverty (and thus into environments that in themselves increase risk
for mental illness), while social causation theories reflect a gene-environment
interaction in which genetic risk remains latent unless individuals are exposed
to the stress of poverty, often by situations beyond their control. The distinction
can be important in suggesting different strategies for prevention or treatment.11

Disentangling the effects of social causation and social selection ideally
requires an experimental design that manipulates poverty levels and studies
the effects on mental illness.11 Income experiments,
such as this, have occasionally been done; for example, the New Jersey Negative
Income Tax experiment of the 1960s,12,13 and
its replications.14- 16 However,
none of these studies investigated the effects of relief from poverty on mental
health. Researchers have had to take advantage of retrospective recall,17 nonexperimental prospective studies,18 or
at best quasi-experimental situations such as the depression of the 1930s,19 the farm crisis of the 1980s,20- 22 or
the immigration of European and North African Jews to Israel.10 The
extent to which the association between poverty and mental illness reflects
social causation or social selection is difficult to test using such natural
experiments, because of the difficulty of disentangling movement into or out
of poverty from other characteristics that might have caused the change in
income. Problems of interpretation are compounded if the quasi-experimental
manipulation was unexpected, and if measures before and after change are not
available. A truly experimental manipulation of income that showed an improvement
in children's behavioral symptoms is the Minnesota Family Investment Program,23 but this study was restricted to single-parent families
who were long-term recipients of welfare.

In the middle of an 8-year, community-based study of the development
of mental illness in children, we were confronted with a natural experiment
in which income levels in an entire community were raised. We used this conjunction
of longitudinal evaluation and natural experiment to test the effect of social
causation on the trajectory of child and adolescent psychopathology. We examined
the mental health of children whose families moved out of poverty, compared
with children whose families remained poor despite the intervention and with
those who were never poor. If family poverty caused specific emotional and
behavioral problems in children,1,4,24 then
after poverty was removed these psychiatric symptoms should improve or disappear.

METHODS

Setting and Population

The Great Smoky Mountains Study is a longitudinal study of the development
of psychiatric disorder and need for mental health services in rural and urban
youth.25,26 A representative sample
of 1420 children aged 9, 11, and 13 years at intake was recruited from 11
counties in western North Carolina. Potential participants were selected from
the population of some 20 000 children, using a household equal probability,
accelerated cohort design.27 Over several years
of data collection, each age cohort reaches a given age in a different year,
thus controlling for cohort effects.28

American Indian children were oversampled, to make up 25% of the final
sample. The Eastern Band of Cherokee Indians live on a federal reservation
that extends into 2 of the 11 counties. The tribe has an enrolled membership
of approximately 8000. The final sample consisted of 350 Indian children (81%
of those recruited) and 1070 non-Indian children (80% of those recruited);
92.5% of the latter were white and 7.5% African American. In the analyses,
each individual's contribution was weighted proportionately to his/her probability
of selection into the study, so that the results are representative of the
whole population of children of this age. During the 8 years (1993-2000) of
this ongoing study, 3 children have died, and 6% have completed only 1 interview.
The mean response rate was 83%. Attrition and nonresponse were found equally
in all the ethnic and income groups.

Intervention

Beginning in 1996, tribal members began to receive income from a gambling
casino that opened on the reservation. Under the terms of the agreement with
the casino operators, every man, woman, and child receives a percentage of
the profits, paid every 6 months. Children's earnings are paid into a trust
fund until the age of 18 years. The payment has increased each year, reaching
around $6000 by 2001. The opening of the casino also increased the number
of jobs available, in the casino itself or in surrounding motels and restaurants.
These jobs are available to both Indians and non-Indians, but Indians receive
preference in hiring at the casino itself.

Procedures

Families were interviewed, usually at home, once a year from 1993 through
2000. Parent and child signed informed consent forms. The study and consent
forms were approved by Duke University's institutional review board. Individuals
then were interviewed in separate rooms by different interviewers. All interviewers
were residents of the study area; some were American Indian. Interviewers
had bachelor's degrees but were not clinically licensed. They received 1 month
of training and were under constant quality control, which was maintained
by postinterview reviews of interview schedules, notes, and tape recordings
by supervisors and study faculty.

Measures

Child and Adolescent Psychiatric Assessment. The
Child and Adolescent Psychiatric Assessment29 is
a structured interview for use with both children and parents or guardians
that enables interviewers to determine whether symptoms, as defined in an
extensive glossary, are present or absent, and to code their frequency, duration,
and onset. The Child and Adolescent Psychiatric Assessment scoring algorithms
can be used to generate either diagnoses made using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV),30 or scale scores
that count the number of DSM-IV psychiatric symptoms
relating to any of 29 separate diagnoses or groups of diagnoses. For these
analyses, in addition to DSM-IV diagnoses, scale
scores were created to cover 2 broad categories of symptoms: those occurring
in an emotional disorder (depression or anxiety) and those consistent with
a behavioral disorder (conduct disorder or oppositional defiant disorder).

To obtain relatively stable estimates of symptom scores for each child
over time, we calculated 3 mean 4-year symptom scores for the period before
the casino opened (1993-1996): 1 for all symptoms, and 1 each for behavioral
and emotional symptoms separately. Another 3 symptom scores were calculated
for the 4-year period after the casino opened (1997-2000). These 6 mean symptom
scores served as the primary outcome measure for all analyses. Children also
were classified as having 1 or more emotional disorders or behavioral disorders
in the period before and after the casino opening. Both types of disorder
were entered together into the models to control for comorbidity.31

Classification Variable. The adult respondent
(usually the mother) provided information about total family income and sources
of income (from earnings, welfare, etc) and rank ordered the sources from
the largest to the smallest percentage of total family income. The mean family
income for the 4 years before and the 4 years after the casino opened was
calculated separately. Families were defined as poor if
the mean income for the 4-year period, adjusted for family size and missing
data, was below the federal poverty line for that year, using the Department
of Health and Human Services guidelines (available at http://www.census.gov/hhes/poverty/threshld.html). Results of repeated analyses using the median were very similar.

Families then were classified into 3 groups: (1) persistently poor,
those families below the federal poverty line before and after the casino
opened; (2) ex-poor, those families who moved out of poverty after the casino
opened; and (3) never poor, those families above the poverty line before and
after the casino opened. The fourth possible group, the newly poor (those
families who were not poor before the casino opened but became poor later),
were excluded from all analyses because of the small number of them (n = 8)
among the American Indian families.

Analyses

We applied a marginal model approach (generalized estimating equations)
to the analysis of these longitudinal data. Generalized estimating equations
is a method developed for dealing with complex longitudinal, repeated, or
clustered data, in which the observations within each cluster are correlated
with each other.32,33 Generalized
estimating equations model the effects of predictors (ie, covariates) on the
marginal expectations (ie, means), while also accounting for the associations
(correlations) among observations from each individual. The parameter estimates
were obtained by minimizing a score function that is a generalization of the
weighted least squares approach. The SAS program PROC GENMOD, version 8.02
(SAS Institute, Inc, Cary, NC) with a Poisson link function was used in the
analyses. In this representative population sample, the number of children
with diagnoses was not large, so symptom scale scores were used for several
of the analyses presented herein. Statistical significance was set at .05.

RESULTS

Association Between Poverty and Psychiatric Disorder

Across the 8 years of the study, a significant negative correlation
between family income and child psychiatric diagnoses (r = −0.13, P<.001) and number of
symptoms (r = −0.15, P<.001)
was observed. The correlation was similar in both non-Indian (r = −0.19, P<.001) and Indian children
(r = −0.17, P<.001).
Children living in poverty were more likely than nonpoor children to have
a psychiatric disorder (22% vs 15%, odds ratio [OR], 1.6; 95% confidence interval
[CI], 1.4-1.8; P<.001). Thus, the data are consistent
with a relationship between poverty and childhood mental illness.

Effects of the Casino on Family Income

Figure 1 shows that whereas
in non-Indian households poverty decreased linearly over the 8 years of the
study at a mean rate of 1%, the percentage of Indian families in poverty increased
between 1993 and 1995, and then decreased 5% between 1997 and 1998, 6% between
1998 and 1999, and 18% between 1999 and 2000. These results show that the
income generated by the casino had an effect on Indian family poverty but
not on non-Indian family poverty from 1996 to 2000.

For American Indian and non-Indian children, the proportion of families
were 53.2% and 20.2% for persistently poor, 14.4% and 10.3% for ex-poor, and
32.4% and 69.5% for never poor, respectively. The casino income did not succeed
in lifting all Indian families out of poverty; more than half (54%) remained
poor throughout the study (compared with only 20% of white children). However,
a higher proportion of Indian than of white families moved out of poverty
after the casino opened (OR, 1.3; 95% CI, 1.1-1.7; P =
.02).

Family Income and Child Mental Illness

We first used the Indian sample to test whether a change in family resources,
indexed by moving above the federal poverty line, had an effect on the likelihood
of psychiatric symptoms. Analyses then were repeated in non-Indian families
who moved out of poverty around the same time. We predicted that we should
see similar results, but the hypothesis that these symptoms were caused by
the increase in income could not be as strong because of possible confounders.

Table 1 shows the mean number
of psychiatric symptoms of any kind in American Indian children, before and
after the casino opened, by poverty group. The cells labeled "contrast" present
the results of 9 between-group pairwise contrasts of interest. For example,
exponentiating the contrast estimate for the comparison between persistently
poor vs never-poor groups during the 4-year period before the casino opened
(eg, e0.463) gives a difference in log odds of approximately 1.59,
suggesting that the odds of having a psychiatric symptom for the persistently
poor group are 59% higher than the odds for the never-poor group. Column contrasts
compare symptom scores across time within a group.

Children of American Indian never-poor and persistently poor families
maintained a steady mean (SD) total number of psychiatric symptoms, low and
high respectively, before and after the casino opened. Children whose families
moved out of poverty, however, showed a significant decrease in the mean number
of psychiatric symptoms after the casino opened (P =
.02).

Between-group comparisons by poverty group revealed that over the 4
years before the casino opened, children whose families were to move out of
poverty had the same number of symptoms as those who were to remain poor,
and both groups had significantly more symptoms than did children whose families
were never poor. The situation changed dramatically after the casino opened.
Between-group comparisons showed that children of ex-poor families had the
same number of psychiatric symptoms as the never poor, and significantly fewer
symptoms than the persistently poor. Thus far, the data supported a social
causation hypothesis, demonstrating a decrease in symptoms in children whose
families moved out of poverty.

We next tested whether the effect of moving out of poverty applied equally
to behavioral and emotional symptoms. Across the whole sample, the mean (SD)
number of behavioral symptoms was almost the same before (2.0 [2.7]) and after
(2.1 [3.2]) the casino opened. Table 2 shows
that this increase was restricted to children from persistently poor families,
whose mean symptom level rose by 21%. Ex-poor children showed a 40% decrease
in behavioral symptoms. Children from never-poor families maintained a steady,
low level of behavioral symptoms before and after the opening of the casino.
Before the casino opened, children from families destined to move out of poverty
had almost as many behavioral symptoms as the persistently poor. After the
casino opened, the mean level of behavioral symptoms in children from ex-poor
families was almost identical to that of never-poor children, and significantly
lower than the mean for persistently poor children (Table 2).

The pattern for emotional symptoms was much less marked (Table 3). Results from the overall Poisson regression showed no
significant interaction between poverty group and time.

Replication in Non-Indian Sample

The social causation theory was subjected to a powerful test in the
Indian community, because the income from the casino came to every family.
No such powerful test of the effect of relieving poverty was available for
the non-Indian families. However, some non-Indian families did move out of
poverty around the same time, after they had been in the study for 4 years,
while others remained poor or were never poor. We repeated the analyses with
non-Indian children, testing the same hypotheses. Results were similar to
those seen in Indian children (Table 4).

How Does Relief of Poverty Affect Children's Psychopathology?

We ran a series of test for mediators of the link between poverty and
psychopathology; that is, factors causally related to the symptoms that could
be affected by relief from poverty. A strict mediational model34 requires
that the significant effect of changing poverty status on the children's symptoms
should become less significant once the putative mediator is entered into
the model; the mediator itself must be significantly associated with poverty
status.

Potential mediators examined were traumatic life events (eg, parent
separation or divorce, sexual or other physical abuse, unplanned pregnancy),
neglect, harsh or inconsistent parenting, overprotective or intrusive parenting,
lax supervision, and maternal depression. Only 1 stressor met the requirements
specified by Baron and Kenny34 as a full mediator:
failure of parents to provide adequate supervision. This stressor was coded
from parents' answers to a set of questions such as, "How often is [the subject]
out without your knowing where s/he is?" Lax supervision is defined as inability to exercise effective control once a week
or more often. As required for a mediational model, the 3 main effects analyses
all were significant in a series of Poisson regressions: the effect of changing
poverty level on the moderator, level of parental supervision (β = −0.59;
SE = 0.14; χ2 = 17.2; P<.001),
effect of changing poverty level on psychiatric symptoms (β = 0.18; SE
= 0.062; χ2 = 8.2; P = .004), and
the effect of supervision on psychiatric symptoms (β = 1.07; SE = 0.13; χ2 = 71.2; P<.001). When the mediational
model was run, including both supervision and changing poverty status, the
effect of changing poverty level on psychiatric symptoms became nonsignificant
(β = 0.04; SE = 0.05; χ2 = 0.59; P =
.44). The mediating effect of parental supervision accounted for approximately
77% of the effect of changing poverty level on the number of psychiatric symptoms
during the 4 years after the opening of the casino. The model produced the
same results for both girls and boys.

In a set of exploratory analyses, we examined differences of 26 variables
between the 3 groups before and after the casino opened that might explain
why parents who were ex-poor were able to maintain better supervision of their
children; factors included single-parent or step-parent household, parental
mental illness, drug abuse or crime, traumatic life events, and lack of time
to spend with child because of other demands (eg, large family or working
2 jobs). Full details can be obtained from the author.

Three of the 26 variables were distinguished among the groups, all having
to do with time constraints in the family. In the ex-poor households, the
number of single-parent households decreased (χ2 = 4.22, P = .04), the number of households with 2 working parents
increased (χ2 = 6.04, P = .01), and
a measure of time demands placed on the index parent decreased (χ2 = 6.74, P = .03). For each of these measures,
the ex-poor families were significantly different from the never-poor families
before the casino opened and were significantly different from the persistently
poor household after it opened.

COMMENT

As Dohrenwend et al10 pointed out a decade
ago,10 "Social causation and social selection
theories both predict an inverse relation between socioeconomic status and
various types of psychopathology. Our problem, therefore, has been to identify
circumstances in which the 2 theories make different predictions."

The present study took a longitudinal approach to the problem, arguing
that if the reason for the well-established association between poverty and
child psychopathology1,4,5,24,35 was
the social selection of mentally ill families into poverty, then relieving
poverty would leave the association intact. If, on the other hand, poverty
had a causal role in the symptoms, then alleviating it would reduce the level
of symptoms. An event that substantially increased the income of every man,
woman, and child in a community provided a natural experiment that we could
use to test these competing models. We found the following: (1) Moving out
of poverty was associated with a decrease in frequency of psychiatric symptoms
over the ensuing 4 years; by the fourth year the symptom level was the same
in children who moved out of poverty as in children who were never poor. (2)
Adding to the income of never-poor families had no effect on frequency of
psychiatric symptoms. (3) The effect of poverty was strongest for behavioral
symptoms (those included in the DSM-IV diagnoses
of conduct and oppositional disorder). Little effect of moving out of poverty
on emotional symptoms (DSM-IV anxiety and depression)
was observed. (4) The effect of relieving poverty was mediated by 1 stressor:
level of parental supervision. (5) The same models run using the non-Indian
participants showed similar results.

These findings thus support a social causation for behavioral problems.
Anxiety and depression symptoms were more common in poor children, but moving
out of poverty was not followed by a reduction in these symptoms. There are
several possible explanations for this. Anxiety and depression in children
and adolescents may be caused by some characteristics of poor families not
directly related to poverty; for example, they may carry a higher genetic
loading for these conditions, as a social selection hypothesis (gene-environment
correlation) would suggest.36 Alternatively,
the remarkable speed of the change in behavioral symptoms after poverty was
lifted may be specific to those symptoms; it might take longer for the reduction
in poverty-induced family stress to be reflected in children's mood and anxiety
levels. In fact, surprisingly little evidence is available linking childhood
anxiety or depression directly to poverty,4,24,37- 39 and
it may be that poverty seriously increases risk for anxiety and depression
only in adulthood.40,41 Effects
on attention-deficit/hyperactivity disorder are not reported here because
the prevalence of attention-deficit/hyperactivity disorder decreased to 0
in all groups as the children moved through adolescence, so there was a confound
between age and the pre- and poststudy design that made the findings uninterpretable.

Theory would predict similar findings in the general population, in
this study represented by the non-Indian children, and indeed the findings
were similar; when families moved out of poverty we saw a reduction in behavioral
symptoms. The problem is with interpretation: did stronger families work their
way out of poverty, did moving out of poverty improve the risk environment
for children, or both? Only an experimental or quasi-experimental design can
disaggregate these 2 possibilities.42

Among the wide range of potential mediators of the effect of poverty
on behavioral symptoms, only parental supervision emerged as a mediator. As
the study participants moved into adolescence, the number of parents who believed
that they provided adequate supervision decreased across the sample, but it
decreased less in the ex-poor than in the persistently poor group. With only
50 children in the ex-poor group, the study lacked power to explore the reasons
for this decrease. However, exploratory analyses showed that the 3 family
characteristics on which the ex-poor families resembled persistently poor
families before the casino opening and never-poor families after the casino
opening all had to do with the amount of time that the index parent had to
pay attention to the child. Like all the other families in the study, the
number of households with 2 parents working full time increased over time,
but ex-poor families reported a reduction in time demands and in the number
of single-parent households (both of which increased in never-poor and persistently
poor households). This finding raises the possibility that children's symptoms,
particularly those of oppositional and deviant behavior, are affected by economic
constraints on parents' ability to devote scarce time resources to supervision.
The fact that 3 significant associations are conceptually linked through their
relationship to family time constraints suggest that our findings are valid.

The Great Smoky Mountains Study has some advantages for addressing the
relationship between poverty and psychopathology. First, the outcomes were
measured in children who played little role in generating the family's social
status, and therefore offered a fairly clean test of competing theories. Second,
the study provided a within-subjects design, following the same children over
an 8-year period; a stronger test than is provided by a between-subjects design.43 Third, this was a representative population sample.
Fourth, the study included a direct manipulation of a key explanatory variable:
an increase in family income in the American Indian families that was not
caused by family characteristics that also could affect children's behavioral
symptoms.

The study also has important limitations. The sample was not large,
and only a small proportion of children (14.4% of Indians, 10.3% of non-Indians)
moved out of poverty. The study lacked power for within-group analyses at
the level of diagnoses, which required us to test for differences at the level
of symptom scales rather than at diagnostic categories. An ethnic difference
correlated 100% with the study intervention. We replicated the findings in
non-Indian families, as a social causation theory would predict, but this
group's income change could not be disentangled from characteristics that
might be causally linked to both moving out of poverty and improved child
mental health. While the rural setting of the study is in some ways an advantage,
in enabling us to disentangle poverty and urban residence, replication in
an urban sample would increase the generalizability of the findings. Most
importantly, the study examined psychiatric symptoms only at the level of
parent- and child-reported phenomena; we could not explore the psychophysiological
processes that changed to bring about a reduction in behavioral symptoms when
the stress of poverty was relieved.

Selection and causation are both compatible with a genetic basis to
psychopathology. Social selection implies a correlation between genes and
environment such that individuals with a genetic liability have difficulty
climbing out of poverty, while social causation implies an interaction: genetic
liability to a disease is expressed under the stress of poverty. Questions
about which genes and about the developmental processes that lead to their
expression in the form of behavioral symptoms are still unanswered.

Lemkau PV. The 1933 and 1936 studies on the prevalence of mental illnesses and
symptoms in the eastern health district of Baltimore, Maryland. In: Weissman MM, Myers JK, Ross CE, eds. Community
Surveys of Psychiatric Disorders. New Brunswick, NJ: Rutgers University
Press; 1986:23-39.